In the case where a solar power system is used to generate electric power, there may be a case where working fluid for driving a steam turbine cannot be heated sufficiently only by solar heat obtained at that time due to the variation or decrease of the amount of solar radiation. To solve this problem, in many examples, a heat storage device is incorporated in the solar power system and heat collected by a heat collection device is stored in advance in the heat storage device so that the stored heat can be extracted and used if necessary (Patent Literatures 1 to 4).